1. Field of the Invention
The present invention relates to a method for creating monocrystalline piezoresistors in the surface of a semiconductor substrate, in which at least one dopant is introduced into the resistance area and in which the resistance area is provided with an electrically insulating sheathing.
2. Description of Related Art
It is known that monocrystalline piezoresistors may be created in a monocrystalline silicon layer by doping the resistance area. Such monocrystalline piezoresistors have a high sensitivity to mechanical stress and also have long-term stability. These piezoresistors are therefore used for signal detection in a number of micromechanical sensor elements, for example, acceleration, force or pressure sensor elements.
In a temperature range below 160° C., piezoresistors in monocrystalline silicon are electrically insulated already just by the depletion zone of the pn-junction between the resistance area and the surrounding silicon. However, with an increase in the ambient temperature, leakage currents occur at this pn-junction. Such piezoresistors are therefore used for measuring purposes only up to an ambient temperature of approximately 160° C. to a maximum of 200° C. At higher temperatures, the leakage currents occurring at the pn-junction lead to an unacceptable distortion of the measurement results.
Published German patent application document DE 10 2008 043 084 A1 proposes embedding the piezoresistor in an oxide area in order to reliably insulate a monocrystalline piezoresistor electrically from the adjacent silicon material, even at higher ambient temperatures. According to published German patent application document DE 10 2008 043 084 A1, the silicon environment of the piezoresistor is therefore initially etched to make it porous, and then the porous etched silicon material is oxidized.